title: Stimulus-induced S-nitrosylation of Syntaxin 4 impacts insulin granule exocytosis.
abstract: Glucose-stimulated insulin release from pancreatic islet β-cells involves increased levels of reactive oxygen and nitrogen species. Although this is normal, under pathophysiological conditions such as chronic hyperglycemia and inflammation, insulin exocytosis fails, and yet the mechanistic reason for failure is unclear. Hypothesizing that exocytotic proteins might be targets of S-nitrosylation, with their dysfunction under conditions of nitrosative stress serving as a mechanistic basis for insulin secretory dysfunction, we identified the t-SNARE protein Syntaxin 4 as a target of modification by S-nitrosylation. The cellular content of S-nitrosylated Syntaxin 4 peaked acutely, within 5 min of glucose stimulation in both human islets and MIN6 β-cells, corresponding to the time at which Syntaxin 4 activation was detectable. S-Nitrosylation was mapped to Syntaxin 4 residue Cys(141), located within the Hc domain predicted to increase accessibility for v-SNARE interaction. A C141S-Syntaxin 4 mutant resisted S-nitrosylation induced in vitro by the nitric oxide donor compound S-nitroso-L-glutathione, failed to exhibit glucose-induced activation and VAMP2 binding, and failed to potentiate insulin release akin to that of wild-type Syntaxin 4. Strikingly, S-nitrosylation of Syntaxin 4 could be induced by acute treatment with inflammatory cytokines (TNFα, IL-1β, and IFNγ), coordinate with inappropriate Syntaxin 4 activation and insulin release in the absence of the glucose stimulus, consistent with nitrosative stress and dysfunctional exocytosis, preceding the cell dysfunction and death associated with more chronic stimulation (24 h). Taken together, these data indicate a significant role for reactive nitrogen species in the insulin exocytosis mechanism in β-cells and expose a potential pathophysiological exploitation of this mechanism to underlie dysfunctional exocytosis.
authors.affiliation: Department of Pediatrics, Herman B. Wells Center for Pediatric Research, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA.
authors.forename: Dean A
authors.initials: DA
authors.lastname: Wiseman
authors.forename: Michael A
authors.initials: MA
authors.lastname: Kalwat
authors.forename: Debbie C
authors.initials: DC
authors.lastname: Thurmond
mesh_terms: D000818:Animals; D016923:Cell Death / Q000187:drug effects / Q000235:genetics; D002460:Cell Line; D005089:Exocytosis; D005947:Glucose / Q000494:pharmacology; D006801:Humans; D007328:Insulin / Q000235:genetics / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D050765:Qa-SNARE Proteins / Q000235:genetics / Q000378:metabolism*; D050600:SNARE Proteins / Q000235:genetics / Q000378:metabolism; D022142:Secretory Vesicles / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D013549:Sweetening Agents / Q000494:pharmacology; D050988:Vesicle-Associated Membrane Protein 2 / Q000235:genetics / Q000378:metabolism
chemical_list: D007328:Insulin; D050765:Qa-SNARE Proteins; D050600:SNARE Proteins; D013549:Sweetening Agents; C494807:VAMP2 protein, human; D050988:Vesicle-Associated Membrane Protein 2; C494808:vesicle-associated membrane protein 2, mouse; D005947:Glucose